18F-FBPA synthesis

¹⁸F-FBPA was prepared following the method of direct radio fluorination of ¹⁰B-BPA, proposed by Ishiwata et al. [15] with a number of modifications, using the F-1 synthesizer (Sumitomo Heavy Industries, Tokyo, Japan).

First, elemental ¹⁸F₂ gas was produced in ²⁰Ne(d,α)¹⁸F reaction and converted to ¹⁸F-acetylhypofluorite in reaction with sodium acetate. ¹⁸F-acetylhypofluorite was bubbled at a flow rate of 600 ml/min into 5 ml of trifluoroacetic acid containing 30 mg of 4-borono-L-phenylalanine, at room temperature. Then, trifluoroacetic acid was removed by passing N₂ under reduced pressure at a flow rate of 200 ml/min. Next, the residue was dissolved in 3 ml of 0.1% acetic acid, and the solution was passed through a high-performance liquid chromatography column YMC-Pack ODS-A (YMC, Kyoto, Japan) 20 × 150 mm, with the flow rate of 10 ml/min and 0.1% acetic acid as a mobile phase. Ultraviolet detector for wavelength 280 nm and radioactivity detector were applied for monitoring of the elution profile. After the ¹⁸F-FBPA fraction was collected (retention time from 19 to 21 min), resultant ¹⁸F-FBPA radiochemical purity was > 98%. The specific radioactivity was 44.1 ± 4.9 GBq/mmol.